Attenuation of poliovirus neurovirulence is the result of a limited number of nucleotide changes in the poliovirus genome. A major site for attenuation (position 472) occurs in a noncoding region of the genome that is involved in the regulation of viral translation. Exactly how (and if) changes in translation result in poliovirus attenuation remain to be established. A recent report by Mola, Paul, and Wimmer, Science 1991;254:1647-1651 suggested that an in vitro translation system derived from HeLa cells translated added poliovirus RNA in a manner that closely mimics the full viral replicative cycle in human cells. We are using this system to determine if wild-type and attenuated genomes exhibit different translational responses in the in vitro extract from a human cell line. HeLa cell extracts have been prepared which respond to the addition of poliovirus RNA by synthesizing poliovirus proteins in vitro. Characteristics of the response to wild type viral RNA are being evaluated and will be used to compare the response to RNA carrying the attenuated phenotype. Elucidation of the role translation plays in the attenuation of poliovirus neurovirulence could lead to further improvements in the stabilization of the attenuation phenotype.